This study examined current thought concerning the role of mass communication in economic development in developing nations; analyzed existing efforts to diffuse agricultural technology in Chile; assessed the effectiveness of various approaches; and tested the effects (primarily on knowledge levels) of an experimental technical information service service for Chilean farmers, as related to variations in land tenure, education, literacy, attitudinal modernity, use of technology, media exposure, and patterns of interpersonal communication. These were among the findings and conclusions: (1) effective programs have offered credit and marketing services as well as technical information; (2) compulsion, in the form of contractual obligations and credit control, appears to hasten adoption; (3) literates, especially opinion leaders, were more active than other groups in secondary diffusion; (4) independent farmers tended to try new practices more than other tenure groups; (5) illiteracy, lack of education, and so-called traditional attitudes were not impenetrable barriers to reception of technical information; (6) personality factors may be less important than other situational variables in determining responses to efforts to introduce new technology. (author/ly)